使用的代码

代码如下:

-- sample data

drop table t_collect purge;

create table t_collect as

select mod(rownum,30) as flag, lpad(dbms_random.string('l',3),4,' ') as val

from dual connect by rownum<=10000;

collect函数(Oracle10g)

-- 1: use collect funtion

select flag,

my_tk.f_list2str(cast(collect(trim(val)) as my_tk_str_tab_type)) as ename

from t_collect sample(10)

group by flag

order by 1;

sys_connect_by_path

-- 2: use sys_connect_by_path and row_number function

select t1.flag, substr(max(sys_connect_by_path(t1.val, ',')), 2) q

from (select a.flag,

trim(a.val) as val,

row_number() over(partition by a.flag order by a.val) rn

from t_collect sample(10) a) t1

start with t1.rn = 1

connect by t1.flag = prior t1.flag

and t1.rn - 1 = prior t1.rn

group by t1.flag

order by 1;

user-defined-function

-- 3: use user-defined-function

select flag,

string_agg(trim(val)) as ename

from t_collect sample(10)

group by flag

order by 1;

辅助用的my_tk包代码片段

代码如下:

create or replace type my_tk_str_tab_type is table of varchar2(100);

---------------------------------------------------------------------

function f_list2str

(

p_list my_tk_str_tab_type,

p_separator varchar2 default ',',

p_sort integer default 1

) return varchar2 is

l_idx pls_integer := 0;

l_str varchar2(32767) := null;

l_spt varchar2(10) := null;

l_list my_tk_str_tab_type := p_list;

begin

if p_sort = 1 then

l_list := f_sort_list(p_list);

end if;

l_idx := l_list.first;

while l_idx is not null loop

l_str := l_str || l_spt || l_list(l_idx);

l_spt := p_separator;

l_idx := l_list.next(l_idx);

end loop;

return l_str;

end;

自定义聚合函数

------------------------------------------------------------------

代码如下:

-- user-defined-function

CREATE OR REPLACE TYPE t_string_agg AS OBJECT

(

g_string VARCHAR2(32767),

STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT t_string_agg)

RETURN NUMBER,

MEMBER FUNCTION ODCIAggregateIterate(self IN OUT t_string_agg,

value IN VARCHAR2 )

RETURN NUMBER,

MEMBER FUNCTION ODCIAggregateTerminate(self IN t_string_agg,

returnValue OUT VARCHAR2,

flags IN NUMBER)

RETURN NUMBER,

MEMBER FUNCTION ODCIAggregateMerge(self IN OUT t_string_agg,

ctx2 IN t_string_agg)

RETURN NUMBER

);

/

CREATE OR REPLACE TYPE BODY t_string_agg IS

STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT t_string_agg)

RETURN NUMBER IS

BEGIN

sctx := t_string_agg(NULL);

RETURN ODCIConst.Success;

END;

MEMBER FUNCTION ODCIAggregateIterate(self IN OUT t_string_agg,

value IN VARCHAR2 )

RETURN NUMBER IS

BEGIN

SELF.g_string := self.g_string || ',' || value;

RETURN ODCIConst.Success;

END;

MEMBER FUNCTION ODCIAggregateTerminate(self IN t_string_agg,

returnValue OUT VARCHAR2,

flags IN NUMBER)

RETURN NUMBER IS

BEGIN

returnValue := RTRIM(LTRIM(SELF.g_string, ','), ',');

RETURN ODCIConst.Success;

END;

MEMBER FUNCTION ODCIAggregateMerge(self IN OUT t_string_agg,

ctx2 IN t_string_agg)

RETURN NUMBER IS

BEGIN

SELF.g_string := SELF.g_string || ',' || ctx2.g_string;

RETURN ODCIConst.Success;

END;

END;

/

CREATE OR REPLACE FUNCTION string_agg (p_input VARCHAR2)

RETURN VARCHAR2

PARALLEL_ENABLE AGGREGATE USING t_string_agg;

/

最后给个参考表

在数据量10000的表上进行三种方法的测试，运行时间单位秒

数据量PCT Collect SYS_Connect UDF

1% 0.017 0.018 0.017

10% 0.026 0.050 0.029

50% 0.057 2.45 0.065

100% 0.090 5.00 1.06

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